1. Field of the Invention
The present invention relates to a plasma tube array which includes an array of two or more light-emitting tubes incorporating fluorescent substance layers therein, produces discharge inside the two or more light-emitting tubes and causes the fluorescent substance layers inside the light-emitting tubes to emit light and thereby displays an image.
2. Description of the Related Art
As a large image display device which performs self light emission, there is a proposal on a technique (see Japanese Patent Laid-Open No. 61-103187) of displaying an image by using the principle of plasma display with an array of multiple light-emitting strings made up of glass tubes incorporating fluorescent substance layers therein and controlling light emission by parts of the respective light-emitting strings (see Japanese Patent Laid-Open No. 61-103187).
Each light-emitting string includes a protective film such as an MgO film and a fluorescent substance layer in the glass tube filled with a discharge gas composed of, for example, Ne and Xe. The fluorescent substance layer is formed on a supporting member, a mounted part, called a “boat”, which has a substantially semicircular cross-section and the supporting member (boat) is inserted into the glass tube. Then, the glass tube is heated in a vacuum chamber and the gas is exhausted, the tube is filled with a discharge gas and then both ends of the glass tube are sealed. Multiple light-emitting strings created in this way are arranged in parallel and fixed and the light-emitting strings are provided with electrodes and a voltage is applied to the electrodes to thereby provoke discharge in the light-emitting strings and cause the fluorescent substance to emit light.
FIG. 1 is a perspective view showing a basic structure of a plasma tube array.
The plasma tube array (PTA) 100 shown here has a structure in which light-emitting strings 10R, 10G, 10B, 10R, 10G, 10B, . . . containing fluorescent substance layers which emit red (R), green (G), blue (B) fluorescence filled with a discharge gas are arranged in parallel and in a planar shape as a whole, and a transparent front supporting member 20 and a transparent back supporting member 30 are placed on the front and back of the light-emitting strings 10R, 10G, 10B, 10R, 10G, 10B, . . . respectively and the array of multiple light-emitting strings 10R, 10G, 10B, 10R, 10G, 10B, . . . are held between the front supporting member 20 and back supporting member 30.
On the front supporting member 20 are multiple display electrode pairs 21 each made up of two display electrodes 211, 212 arranged parallel to each other forming a discharge slit in between in the direction of the array of the multiple light-emitting strings 10R, 10G, 10B, 10R, 10G, 10B, . . . that is, the direction in which the display electrodes extend across the multiple light-emitting strings 10R, 10G, 10B, 10R, 10G, 10B, . . . . These display electrode pairs 21 are arranged in two or more rows in the longitudinal direction of the light-emitting strings 10R, 10G, 10B, 10R, 10G, 10B, . . . forming a non-discharge slit between the neighboring display electrode pairs 21. Furthermore, the two display electrodes 211, 212 making up one display electrode pair 21 consist of metallic (e.g., Cr/Cu/Cr) bus electrodes 211a, 212a on the mutually far sides (non-discharge slit sides) and transparent electrodes 211b, 212b each made up of an ITO thin film on the mutually near sides (discharge slit sides). The bus electrodes 211a, 212a are intended to reduce the electric resistance of the display electrodes 211, 212 and the transparent electrodes 211b, 212b are designed so as to allow light emitted from the light-emitting strings 10R, 10G, 10B, 10R, 10G, 10B, . . . to pass through up to the front supporting member 20 side without being intercepted and thereby realize brighter display.
Furthermore, on the back supporting member 30 are multiple metallic signal electrodes 31 which are associated with and extend parallel to the multiple light-emitting strings 10R, 10G, 10B, 10R, 10G, 10B, . . . respectively.
When the PTA 100 having such a structure is viewed two-dimensionally, the intersections between the signal electrodes 31 and display electrode pairs 21 become unit light-emitting regions (unit discharge regions). Display is realized by using either one of the display electrode 211, 212 as a scanning electrode, producing a selective discharge at the intersection between the scanning electrode and signal electrode 31 to select a light-emitting region, using wall charge formed on the inner surface of the light-emitting string of the region accompanying the discharge and thereby generating a display discharge between the display electrodes 211, 212. A selective discharge is an opposed discharge produced in the light-emitting string between the opposed scanning electrode and signal electrode 31 in vertical direction, while a display discharge is a planar discharge produced in the light-emitting string between the display electrodes 211, 212 arranged in parallel on a plane. Such an electrode arrangement causes two or more light-emitting regions to be formed inside the light-emitting string in the longitudinal direction.
FIG. 2 is a schematic view showing the structure of light-emitting strings making up the PTA 100 shown in FIG. 1.
Here, three light-emitting strings 10R, 10G, 10B are shown. Each of the light-emitting strings 10R, 10G, 10B has a structure in which a protective film 12 of MgO, etc., is formed on the inner surface of a glass tube 11 and a boat 13 which is a supporting member on which fluorescent substance layer 14R, 14G, 14B emitting R, G, B fluorescence is formed is inserted in the glass tube 11 (see Japanese Patent Laid-Open No. 2003-86141).
FIG. 3 shows the boat on which the fluorescent substance layer is formed.
The boat 13 has a semicircular or U-figured cross-section or the like and has an elongated shape as with the glass tube 11 (see FIG. 2) and each of three types of fluorescent substance layers 14R, 14G, 14B (see FIG. 2: here represented by the fluorescent substance layer 14) corresponding to the three type of light-emitting strings 10R, 10G, 10B shown in FIG. 1, FIG. 2 is formed on the inside thereof.
Returning to FIG. 2, the explanation will be continued.
Each of the light-emitting strings 10R, 10G, 10B shown in FIG. 2 has a structure in which the boat 13 having the shape shown in FIG. 3 is inserted in the glass tube 11. FIG. 2 shows the display electrode pair 21 made up of the two display electrodes 211, 212, between which a discharge slit is formed, is arranged on the light-emitting strings 10R, 10G, 10B. The two display electrodes 211, 212 are made up of metallic bus electrodes 211a, 212a and transparent electrodes 211b, 212b. 
Here, in the case of the structure shown in FIG. 2, a region D1 defined by one set of the three light-emitting strings 10R, 10G, 10B provided with the three types of fluorescent substance layers 14R, 14G, 14B respectively and one display electrode pair 21 made up of the two display electrodes 211, 212 constitutes one pixel which is a unit for displaying a color image. The diameter of each light-emitting string 10R, 10G, 10B is typically on the order of 1 mm, and therefore in the case of the structure shown in this FIG. 2, the size of the region D1 of one pixel is about 3 mm×3 mm.
In the PTA having the basic structure described above, instead of arranging light-emitting strings two-dimensionally, it is also possible to form a curved image display plane by arranging the light-emitting strings along a curve (see Japanese Patent Laid-Open No. 2003-92085) or make the image display plane flexibly modifiable into various types of curved surfaces.
In such a case, a flexible substrate, for example, PET (polyethylene terephthalate) substrate is used as the front supporting member 20 and back supporting member 30 and the display electrodes 211, 212 formed on the front supporting member 20 are also required to have a structure resistant to bending. In this case, when the display electrodes 211, 212 combining the metallic bus electrodes 211a, 212a and transparent electrodes 211b, 212b each made up of an ITO thin film as explained with reference to FIG. 1, FIG. 2 are used, since the ITO thin film has poor ductility, it may be cracked or subject to breaks when the flexible substrate is bent. For this reason, instead of the transparent electrodes 211b, 212b made of the ITO thin film, there is a proposal on an electrode structure with metal thin wires wired in a mesh, ladder stitch, or comb-like pattern (Japanese Patent Laid-Open No. 2003-338244). The electrodes having wiring of these metal thin wires are more appropriate in the sense that they are resistant to bending of the substrate and that the image display plane is formed on a flexible curved surface.
FIG. 4 is a schematic diagram showing an example of display electrodes using metal thin wires.
The figure shows a display electrode pair 21 made up of two display electrodes 211, 212 with a discharge slit 210 formed in between and the respective display electrodes 211, 212 are made up of bus electrodes 211a, 212a which are also provided for the display electrodes shown in FIG. 1, FIG. 2 and branched electrodes 211c, 212c made up of mesh-like metal thin wires 611, 612 instead of the transparent electrodes 211b, 212b shown in FIG. 1, FIG. 2. In these branched electrodes 211c, 212c, multiple openings 621, 622 surrounded by the metal thin wires 611, 612 are formed, distributed over all the branched electrodes 211c, 212c. 
When the display electrodes 211, 212 having the structure shown in FIG. 4 as well as the display electrodes using the transparent electrodes 211b, 212b shown in FIG. 1, FIG. 2, a discharge produced in the discharge slit 210 provokes a discharge inside the light-emitting string 10 (called light-emitting string 10 as representative of light-emitting strings 10R, 10G, 10B) shown in FIG. 2 and causes the fluorescent substance 14 therein to emit light.
Light emitted from this fluorescent substance passes through the discharge slit 210 or the openings 621, 622 of the branched electrodes 211c, 212c and appears as an image when the entire display surface is viewed.